Physicians in the UK were unable to explain a strange ring-like pattern moving across a patient's brain tissue in a series of scans taken over four years. During a biopsy, they were shocked to learn it was a one centimeter-long parasitic tape worm.

The 50-year-old Chinese man was admitted to hospital after complaining of headaches, memory flashbacks, and experiencing strange smells. The rare parasitic tapeworm Spirometra erinaceieuropaei was found to have burrowed from one side of the man's brain to the other.

According to geneticists at Wellcome Trust Sanger Institute in Cambridge, the tapeworm, which is normally found in China, is known to infect dogs, frogs, and cats. Only 300 human infections have been reported since 1953, and none of them in the brain. The Guardianreports:

After visiting his doctor, an MRI scan revealed a cluster of rings in the right medial temporal lobe.

He was given tests for a wide range of other diseases including syphilis, HIV and tuberculosis but tested negative for them all. Later scans showed the rings moving through his brain.

After undergoing two biopsies, surgeons found the worm moving around in his brain and removed it in 2012. The man was then given drugs to help treat the infection but he continues to suffer from problems associated with having had the worm living in his brain.

It is not known how he first became infected, but one source of infection is the use of frog poultice, a traditional Chinese remedy where raw frog meat is used to calm sore eyes.

"We did not expect to see an infection of this kind in the UK, but global travel means that unfamiliar parasites do sometimes appear," said Dr Effrossyni Gkrania-Klotsas, one of the clinicians involved in the man's treatment at Addenbrooke's NHS Trust.

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While in the brain, the worm triggered inflammation, which is what caused the patient's symptoms. To survive, the parasite likely absorbed nutrients such as fats directly through its skin. And in fact, the brain happens to be rich in fatty acids — which may explain why the worm survived for four years.

The geneticists say the parasite's genome has around 10 times more DNA than any other tapeworm sequences so far, which may explain its ability to invade many different species.